I recently invested in a collapsible, rolling ice chest, brightly-colored melamine plates and a small cutting board. I already had a small BBQ, wicker picnic basket, and a giant wine collection (no, seriously...you'd think we were winos.) It's helpful to bring a trash bag, ziploc bags for used utensils, a wind bottle opener (very sad when you leave this behind,) wet naps for sticky hands, and sunscreen! I always keep a picnic blanket in my trunk because you never know when you'll need something to sit on or cover up with. And it made perfect sense to me to start making some picnic blankets for our Etsy store. My first batch sold out quickly, but I've recently added more.
So start planning your own picnic! Here are some SF links to help: